DESCRIPTION( provided by the applicant): The long-term objective of this proposal is to generate a molecular understanding of the developmental roles of a "prototype" of chromatin regulators- Ikaros, Aiolos and Mi-2beta- to help answer fundamental questions about how B cell differentiation and proliferation is controlled. The developmentally regulated DNA binding factors, Aiolos and Ikaros, are present in a lymphoid-specific version of an otherwise ubiquitous chromatin-remodeling complex (NURD). This suggests that they target this complex in a lineage-specific fashion to provide a cascade of regulatory events required for entry and differentiation into the B cell lineage. In the first specific aim, we will study the effects of Ikaros and Aiolos deficiency on early hemopoietic progenitors and their ability to become restricted along the lymphoid pathway. A search for progenitors with lymphoid properties will be performed. These cells will be examined for molecular defects that prevent entry into the B cell pathway. In the second specific aim we will investigate the role of Ikaros in combination with Aiolos at subsequent stages of B cell differentiation, including commitment and maturation to an antigen-specific B cell. Their effect on key molecular events that support progression through the pathway will be examined. For the third specific aim, Ikaros levels will be raised in early hemopoietic progenitors, and the effect on molecular responses associated with lymphoid-lineage differentiation will be examined. In the fourth specific aim, the role of the NURD-chromatin remodeller,Mi-21], in B cell differentiation will be determined using inducible and B cell-specific inactivation strategies. These studies will provide a functional link between the NURD complex and the Ikaros gene family during B cell development and function. The proposed studies will, on one hand, provide novel insights on the regulation of B cell developmental transitions by this complex of chromatin regulating factors and, on the other hand, reveal underlying gene targets and mechanisms of action. Since deficiencies in the Ikaros gene family cause immune disorders that range from immunodeficiency to leukemias/lymphomas to autoimmune syndromes, an important outcome of these studies will be an increase in our ability to apply molecular intervention to these differentiation processes.